Pavement markings convey information to drivers and pedestrians by providing exposed visible, reflective and/or tactile surfaces that serve as indicia upon a traffic surface. In the past such a function was typically accomplished by painting a traffic surface. Modern pavement marking materials offer significant advantages over paint such as dramatically increased visibility and/or retroreflectance, improved durability, and temporary removable marking options. Examples of modern pavement marking materials are thermoplastic, pavement marking sheet materials, tapes and raised pavement markers.
The Americans with Disabilities Act of 1990, published requirements for sidewalk and other potentially dangerous areas in that detectable warning devices would be required to warn blind or visually impaired and wheelchair bound individuals of potentially dangerous and vehicular traffic areas. Of particular note is section 4.29, §§0.2 as restated below:
4.29 Detectable Warnings:
                4.29.2 Detectable Warnings on Walking Surfaces. Detectable warnings shall consist of raised truncated domes with a diameter of nominal 0.9 in (23 mm), a height of nominal 0.2 in (5 mm) and a center-to-center spacing of nominal 2.35 in (60 mm) and shall contrast visually with adjoining surfaces, either light-on-dark, or dark-on-light. The material used to provide contrast shall be an integral part of the walking surface. Detectable warnings used on interior surfaces shall differ from adjoining walking surfaces in resiliency or sound-on-cane contact.        4.29.3 Detectable Warnings on Doors to Hazardous Areas.        4.29.4 Detectable Warnings at Stairs.        4.29.5 Detectable Warnings at Hazardous Vehicular Areas. If a walk crosses or adjoins a vehicular way, and the walking surfaces are not separated by curbs, railings, or other elements between the pedestrian areas and vehicular areas, the boundary between the areas shall be defined by a continuous detectable warning which is 36 in (915 mm) wide, complying with 4.29.2.        4.29.6 Detectable Warnings at Reflecting Pools. The edges of reflecting pools shall be protected by railings, walls, curbs, or detectable warnings complying with 4.29.2.        
Detectable warning devices may be constructed as a preformed thermoplastic, thermoplastic, rubber, adhesive tile, tile cast into concrete, metal or other suitable material that will withstand abrasion and environmental extremes.
Formulations for preformed thermoplastic detectable warning devices, pavement markings and traffic control devices (preformed thermoplastic signage) are generically comprised of a:                Binder (˜20%) containing:                    Resin:                            Maelic modified resin ester                C5 hydrocarbon, (for hydrocarbon class)                Rosin ester (for alkyd class)                Plasticizer                Vegetable oils                Phthalate esters                Mineral oil                Castor oil                Wax/Flexibilizer                Paraffin wax                Polyamide                EVA or SBS elastomers                                    Pigment (2-10%):                            Titanium dioxide                Lead chromate                Organic dyes                Filler (30-40%)                Calcium carbonate                Glass beads (30-40%)wherein the thermoplastic signage may be alkyd or hydrocarbon based and includes a hot melt thermoplastic application. Thermoplastic signage must meet the standard specifications as published in the AASHTO (American Association of State Highway Transportation Officials) Designation: M 249-98.                                                
Continuous and skip lane striping's on highways and pedestrian crosswalk markings employ preformed pavement marking sheeting preferably comprising a wear-resistant top layer optionally overlying a flexible base sheet. The top layer is generally highly visible, may include retroreflective elements to enhance detection when illuminated by traffic at night, and serves as indicia when installed upon the roadway surface. Application of temporary pavement marking sheeting to a traffic surface has typically been by contact cement or rubber-based pressure-sensitive adhesives. Traffic surfaces may include surfaces for pedestrians, motorized vehicles, aircraft, human powered conveyances, programmable robotics and the like.
Another example of a pavement marking is a raised pavement marker (i.e. a discreet marking structure with a rigid, semi-rigid or flexible marking body) which when applied to a roadway surface provides a raised surface. Often, the raised surface is both reflective and strategically oriented to enhance reflective efficiency when illuminated by traffic at night. In the case of rigid discreet markers, attachment of the body of each marker to the pavement surface has involved hot-melt adhesives or epoxy systems. Flexible body raised pavement markers have also been attached to pavement surfaces or pavement marking sheeting by soft butyl mastic materials.
In order to fulfill their function as indicia, both raised thermoplastic detectable warning devices, pavement markers and pavement marking sheeting must be applied to a rather troublesome substrate. That substrate, the traffic surface, varies widely in terms of surface properties because the underlying material may be concrete or asphalt, may be of varying age and temperature, and may, on occasion, be moist or damp or oily. Additionally, the roadway surface may vary in texture from rough to smooth. The substrate surface properties, therefore, represent a considerable challenge for attachment.
Specifically the standard for thermoplastic marking bond strength can be found in ASTM D4796-(2004), which states the test method and bonding strength of thermoplastic signage to concrete as: Bond Strength—After heating the thermoplastic material for four hours at 425 degrees F. the bond strength to Portland Cement Concrete shall exceed 1.24 Mpa (˜180 psi). Preferably the bond strength is from about 200 psi to about 500 psi.
Thermoplastic signage therefore must reach a softening point within a range of about 400 degrees F. to about 450 degrees F. as determined by the ring and ball softening point test method specified in AASHTO Designation: M 249-98, section 12.
Concrete is a mixture of paste and aggregates. The paste, composed of Portland cement and water, coats the surface of the fine and coarse aggregates. Through a chemical reaction called hydration, the paste hardens and gains strength to form the rock-like mass known as concrete. Within this process lies the key to a remarkable trait of concrete: it is plastic and malleable when newly mixed, strong and durable when hardened. These qualities explain why concrete, can build superhighways, sidewalks, bridges, warehouse flooring, and other traffic media.
All Portland cements are hydraulic cements that set and harden through a chemical reaction with water. During this reaction, called hydration, a node forms on the surface of each cement particle. The node grows and expands until it links up with nodes from other cement particles or adheres to adjacent aggregates.
Curing begins after the exposed surfaces of the concrete have hardened sufficiently to resist marring. Curing ensures the continued hydration of the cement and the strength gain of the concrete. Concrete surfaces are cured by sprinkling with water fog, or by using moisture-retaining fabrics such as burlap or cotton mats. Other curing methods prevent evaporation of the water by sealing the surface with plastic or special sprays (curing compounds).
Some of the deficiencies associated with present pavement marking adhesion include the: (1) inability for signage to be adhered to uncured concrete which, depending on conditions, may take from about 8 days to about 21 days up to six months to exhibit a sufficient bonding surface, (2) inability to be applied due to limited adhesive tack at low temperature; (3) limited ability to accommodate surface roughness; (4) reduced durability, particularly at low temperature, when subjected to impact or shear; (5) increasing adhesion over time which in turn limits the duration of a period during which a temporary installation may be efficiently removed; and (6) staining of light colored concrete roadway surfaces by adhesives in removable markers.
Generally, the application of the thermoplastic or preformed thermoplastic signage requires that the concrete substrate be cured minimally from about 8 days to about 21 days before the application of the thermoplastic or preformed thermoplastic signage with some products requiring up to six months. Most preformed thermoplastic signage require the concrete substrate to be preheated to bring the concrete surface substrate up to a required temperature prior to application of the preformed thermoplastic signage. The signage is then heated over the pre-heated concrete surface to melt the signage into the porous surface of the concrete substrate. It is an additional feature of the present invention that this preheating requirement is avoided.
Where the traffic site is newly constructed concrete, the contracted signage application presently adds days to the completion of the project in that the application of thermoplastic detectable warning devices and pavement markers must have a cured surface to adhere to. In most concrete pedestrian traffic areas the concrete is ready for pedestrian traffic from about 72 hours to about 96 hours whereas the signage requires greater curing time for permanent application thereby leaving the traffic area non-ADA compliant.
Laitance (residual from concrete curing process) on the concrete surface must be removed and cleaned prior to application of the thermoplastic signage. Such residual is cleaned from the concrete surface via grinding or high pressure washing, leaving the concrete top surface wet. Most signage and adhesives require a clean dry surface for preferred adhesion properties. It is also an additional feature of the present invention that laitance removal is not required to establish a good bond to the Portland cement substrate.
Polyurea coatings may also be comprised of aspartic esters which provide amine functionality and a chemical backbone containing amine linkages. Polyurea is generally used as an industrial coating in severe environments such as with wet or damp surfaces with good chemical resistance to hydrocarbons. Polyurea systems may be applied via spray, 2-part caulk, pour, brush-on or other methods known to those skilled in the art.
In many cases, people tend to mix up polyurea coatings and polyurethane coatings. Thus polyurethane coatings have become a generic term for coating systems based on polyisocyanate reactions. Polyurea coatings normally use amines as coreactants to react with isocyanates. This reaction is extremely fast (within a few seconds or minutes). As a result, polyurea coatings tend to have a very limited pot life and their recoat time becomes a problem in cases where multiple coats are required. A polyurea linkage, however, will have better heat and high temperature resistance than a polyurethane system with polyols as coreactants (post-curing).
Polyurea can be defined as the result of a chemical reaction between an isocyanate and an amine. These amines are generally comprised of polyetheramines and a primary amine chain-extender which is used to impart hard block content and place the formulation on a volume ratio of about 1:1.
This two-component technology is based on an isocyanate quasi-prepolymer and an amine coreactant. Often an amine resin blend polyurea elastomer is made from an (A) component and a (B) component, where the (A) component has a quasi-prepolymer made from an isocyanate and an active hydrogen-containing material, such as a poly-oxyalkylenepolyamine, as described in U.S. Pat. No. 5,442,034 to Dudley J. Primeaux, II of Huntsman Petrochemical Corporation and herein incorporated by reference. The (B) component includes an amine resin, such as an amine-terminated polyoxyalkylene polyol which may be the same or different from the polyoxyalkylene poly-amine of the quasi-prepolymer. The viscosity of the (A) component is reduced by the inclusion of an organic, alkylene carbonate, such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate and the like. The alkylene carbonate also serves as a compatibilizer between the two components, thus provided an improved mix of the system.
Preferably a two-part low viscosity adhesive would comprise a Part (A) component of about 300 centipoise (cp) and a Part (B) component of about 100 centipoise in an add mixture blend of about 250 centipoise.
U.S. Pat. No. 4,532,274, to Spurr, and assigned to Union Carbide, hereby incorporated by reference, describes epoxied formulations and reactions. An illustration of suitable cycloaliphatic epoxides are as follows:
Formula I
Diepoxides of cycloaliphatic esters of dicarboxylic acids having the formula:
wherein R1 through R9, which can be the same or different are hydrogen or alkyl radicals generally containing one to nine carbon atoms inclusive and preferably containing one to three carbon atoms inclusive as for example methyl, ethyl, n-propyl n-butyl, n-hexyl, 2-ethylhexyl, n-octyl, n-nonyl and the like; R is a valence bond or a divalent hydrocarbon radical generally containing one to nine carbon atoms inclusive and preferably containing four to six carbon atoms inclusive, as for example, alkylene radicals, such as trimethylene, tetramethylene, pentamethylene, hexamethylene, 2-ethylhexamethylene, octamethylene, nonamethylene, and the like; cycloaliphatic radicals, such as 1,4-cyclohexane, 1,3-cyclohexane, 1,2-cyclohexane, and the like.
Particularly desirable epoxides, falling within the scope of Formula I, are those wherein R1 through R9 are hydrogen and R is alkylene containing four to six carbon atoms.
Among specific diepoxides of cycloaliphatic esters of dicarboxylic acids are the following:    bis(3,4-epoxycyclohexylmethyl)oxalate,    bis(3,4-epoxycyclohexylmethyl)adipate,    bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate,    bis(3,4-epoxycyclohexylmethyl)pimelate,and the like. Other suitable compounds are described in U.S. Pat. No. 2,750,395 to B. Phillips et al.Formula II
A 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate having the formula:
wherein R1 through R9 which can be the same or different are as defined for R1 in formula I. Particularly desirable compounds are those wherein R1 through R9 are hydrogen. Among specific compounds falling within the scope of Formula II are the following: 3,4-epoxycyclohexylmethyl, 3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-1-methylcyclohexylmethyl, 3,4-epoxy-1-methylcyclohexylmethyl, 3,4-epoxy-1-methylcyclohexanecarboxylate, 6-methyl-3,4-epoxycyclohexylmethyl, 6-methyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-3-methylcyclohexylmethyl, 3,4-epoxy-3-methylcyclohexanecarboxylate, 3,4-epoxy-5-methylcyclohexylmethyl, 3,4-epoxy-5-methylcyclohexanecarboxylate. Other suitable compounds are described in U.S. Pat. No. 2,890,194 to B. Phillips et al.Formula III
Diepoxides having the formula:
wherein the R single and double primes, which can be the same or different, are monovalent substituents such as hydrogen, halogen, i.e., chlorine, bromine, iodine or fluorine, or monovalent hydrocarbon radicals, or radicals as further defined in U.S. Pat. No. 3,318,822 to Hans Batzer et al. Particularly desirable compounds are those wherein all the R's are hydrogen.
Other suitable cycloaliphatic epoxides are the following:
and the like.
The preferred cycloaliphatic epoxides are the following:    3,4-Epoxycyclohexylmethyl-3,4-Epoxycyclohexanecarboxylate
    Bis-(3,4-Epoxycyclohexylmethyl) Adipate
    2-(3,4-Epoxycyclohexyl-5,5,spiro-3,4-epoxy) cyclohexane-meta-dioxane
    vinyl cyclohexane Dioxide
or mixtures thereof.
Epoxides with six membered ring structures may also be used, such as diglycidyl esters of phthalic acid, partially hydrogenated phthalic acid or fully hydrogenated phthalic acid. Diglycidyl esters of hexahydrophthalic acids being preferred. Mixtures of epoxide resins may also be used.
The glycols suitable for use in this invention include polycaprolactone polyols as well as alkylene oxide adducts of polyhydroxyalkanes. Illustrative of the polycaprolactone polyols that can be used one can mention the reaction products of a polyhydroxyl compound having from 2 to 6 hydroxyl groups with caprolactone. The manner in which these polycaprolactone polyol compositions are produced is shown in, for example, U.S. Pat. No. 3,169,945 and many such compositions are commercially available. In the following table there are listed illustrative polycaprolactone polyols. The first column lists the organic functional initiator that is reacted with caprolactone and the average molecular weight of the polycaprolactone polyol is shown in the second column.
Knowing the molecular weights of the initiator and of the polycaprolactone polyol one can readily determine the average number of molecules of caprolactone (CPL Units) that reacted to produce the compound; this figure is shown in the third column.
POLYCAPROLACTONE POLYOLSAverageAverage No.Initiator of polyol in moleculesMWof CPL Units1Ethylene glycol29022Ethylene glycol8036.53Ethylene glycol2,114184Propylene glycol87475Octylene glycol60246Decalence glycol8015.57Diethylene glycol5273.78Diethylene glycol8476.59Diethylene glycol1,2461010Diethylene glycol1,99816.611Diethylene glycol3,5263012Triethylene glycol7545.313Polyethylene glycol (MW 200)*7134.514Polyethylene glycol (MW 600)*1,396715Polyethylene glycol (MW 1500)*2,86812161,2-Propylene glycol6465171,3-Propylene glycol988818Dipropylene glycol476319Polypropylene glycol (MW 425)*8243.620Polypropylene glycol (MW 1000)*1,684621Polypropylene glycol (MW 2000)*2,456422Hexylene glycol9167232-Ethyl-1,3-hexanediol6024241,5-Pentanediol4463251,4-Cyclohexanediol6294.5261,3-Bis (hydroxyethyl)-benzene736527Glycerol5484281,2,6-Hexanetriol476329Trimethylolpropane590430Trimethylolpropane7615.431Trimethylolpropane1,1038.532Triethanolamine8906.533Erythritol920734Pentaerythritol1,2199.5*= Average molecular weight of glycol.
The structures of the compounds in the above tabulation are obvious to one skilled in the art based on the information given. The structure of compound No. 7 is:
wherein the variable r is an integer, the sum of r+r has an average value of 3.7 and the average molecular weight is 527. The structure of compound No. 20 is:
wherein the sum of r+r has an average value of 6 and the average molecular weight of 1,684. This explanation makes explicit the structural formulas of compounds 1 to 34 set forth above.
Illustrative alkylene oxide adducts of polyhydroxyalkanes include, among others, the alkylene oxide adducts of ethylene glycol, propylene glycol, 1,3-dihydroxypropane, 1,3-dihydroxybutane, 1,4-dihydroxybutane, 1,4-1,5- and 1,6-dihydroxyhexane, 1,2-, 1,3-, 1,4-, 1,6-, and 1,8-dihydroxyoctane, 1,10-dihydroxydecane, glycerol, 1,2,4-trihydroxybutane, 1,2,6-trihydroxyhexane, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, pentaerythritol, caprolactone, polycaprolactone, xylitol, arabitol, sorbitol, mannitol, and the like; preferably the adducts of ethylene oxide, propylene oxide, epoxybutane, or mixtures thereof. A preferred class of alkylene oxide adducts of polyhydroxyalkanes are the ethylene oxide, propylene oxide, or mixtures thereof, adducts of trihydroxyalkanes. The preferred alkylene oxide adducts of polyhydroxyalkanes are of the following formula:
wherein R10 is alkane of 3 to 10 carbon atoms, preferably 3 carbon atoms, and n is an integer of from about 4 to about 25.
It is customary to add appropriate hardeners to epoxide compositions to effect cure. Among suitable hardeners are the following: 1. polybasic acids having at least 2 carboxylic acid groups per molecule. 2 anhydrides of acids having at least 2 carboxylic acid groups per molecule.
Illustrative of suitable polybasic acids are the polycarboxylic acids of the formula:HOOC—(CH2)f—COOHwherein f is an integer generally having a value of from 1 to 20 inclusive, as for example, malonic, glutaric, adipic, pimelic, suberic, azelaic, sebacic and the like. Other examples of suitable acids are phthalic acid, isophthalic acid, terephthalic acid, hexahydrophthalic acid, and the like. Further acids are enumerated in U.S. Pat. No. 2,918,444 to B. Phillips et. al.
Among other suitable polybasic acids, having at least two carboxylic groups per molecule, can be noted the following: tricarballylic acid, trimellitic acid and the like. Other such suitable polybasic acids, including polyesters thereof, are described in U.S. Pat. No. 2,921,925 to B. Phillips et al.
Suitable anhydrides are the anhydrides of the acids listed above.
For purposes of stoichiometric calculations with respect to acids, one carboxyl group is deemed to react with one epoxy group; with respect to anhydrides, one anhydride group is deemed to react with one epoxy group. The curable epoxy comprises a one part or multiple part composition or mixture and the mixture is optionally a isocyanate-functional prepolymer, an effective amount of terpene phenolic resin, and an effective amount of a silane compound.
Preferred hardeners include methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride and methylhexahydrophthalic anhydride.
In an embodiment of this invention, the hardener such as the anhydride may be reacted with the glycol and this reacted product added to the epoxide.
It is to be understood that other additives can be added to the compositions of this invention as is well known in the epoxy art. These additives include the following: modifiers such as dimer acid (made from unsaturated C18 fatty acids and is a mixture of 3 percent mono basic acids, 75 percent dimer acid and 22 percent trimer acid and sold under the name of Empol 1022 by Emery Industries), a carboxyl terminated butadiene acrylonitrile (80-20) random copolymer having a molecular weight of about 3300; fillers such as clay, silica, aluminum trihydride, or mixtures thereof which may be coated with, for example, silanes, which fillers may be added in amounts of up to about 60 percent; pigments such as carbon black; mold release agents, and the like.
The compositions of this invention are prepared by simply mixing the epoxide, glycol, catalyst, hardener and other ingredients at room or higher temperatures in a suitable container. Also, the epoxide and glycol may be mixed in one container and the hardener, catalyst and/or accelerator in another container and these two mixed.
The composition is then heated in order to effect its cure. The temperature to which the composition of this invention are heated to effect cure will, of course, vary and depend, in part upon the exact formulations of the composition. Generally, temperatures in the range of about 100° C. to about 200° C. are used for a period of time ranging from about 1 to about 6 hours.
The compositions of this invention are preferably used to fabricate thermoset resin articles by the procedure as set forth in U.S. patent application Ser. No. 430,366, filed in the names of R. Angell et al., titled “A Process For Fabricating Thermoset Resin Articles” and filed on the same data as this application. The process described in said application Ser. No. 430,366 comprises the steps of (a) providing in an accumulator zone, a liquid body of an epoxide containing organic material which is curable upon heating to a thermoset resin composition, the viscosity of said liquid body being maintained essentially constant in the accumulator zone by keeping its temperature below that at which curing of said materials is substantial, (b) providing a heated closed mold from which essentially all of the air has been removed from the cavity in said mold, (c) injecting at least a portion of said liquid body under pressure into the closed mold to fill the cavity in the mold, (d) initiating the curing of said materials by subjecting the materials to a temperature in the mold above the temperature at which the curing of said materials is initiated, (e) maintaining a pressure on the curing material, (f) injecting additional of said materials to the mold cavity during the curing of said materials, and (g) opening said mold and removing the article therefrom.
Other processes known in the art may be used to formulate the compositions of this invention.